Production of chemical pulp, etc.



`March 10, 1931. 1 BRADLEY ET Al.

PRODUCTION OF CHEMICAL PULP, ETC

Filed sept. 2, 1926 ATTORNEYS Patented Mar. lv10, 1931 UNITI-:D` STATES PATENT vOFFICE LINN BRADLEY, OE MONTCLATE, NEW JERSEY, AND EDWARD r. MCKEEFE, OE PLATTS- BURG, NEW YORK, AssIGNORs-TO ERADLEY-MCKEEEE CORPORATION, OE. NEW YORK,

N. Y.,YA CORPORATION F NEW YORK PRODUCTION OF CHEMICAL PULP, ETC.

Application filed September 2, 1926. Serial No. 133,289.

'lhis invention relates to the production of chemical pulp, and to the treatment of residual liquors for the regeneration of cooking liquors.

` More particularly the invention relates to cyclic and interrelated operations, in Which two or more 'different kinds or types of sulfur-containing cookingliquors are employed,

of some of the same soda as a suliite in onetype and as sullidl'in another type of liquor, although thesoda and the sulfur may in part be present as other compounds.

' Among the particular improvements which,

the invention presents are operations or steps',

employing interrelated acid-sullite processes and s'ulfid processes, in which cooking liquors for one type of cooking process are regenerated (at least in part) from residual liquors of another type of cooking process, and vice versa. The acid sul'fite cooking processes to which the invention particularly relates are those in which a relatively high content of 'combined sullite is employed, more particu' larly cooking liquors in Which the combined sodium is equal to or greater than that corresponding to sodium-bisulfite, the cooking liquors being free from any large excess of sulfur dioxide or sulfurous acid and general being made upj'oii` mixtures of sodium monosuliite and sodium bisulite. The sulfid type of cookingliquors to which the invention more particularly relates are regenerated cooking liquors .in Which the sodium present as sodium suld equals yor exceeds in amount that presentas sodium hydroxide,

in case the latter also -is present.

According to one embodiment of the present invention, residual liquor from an acid sullite cooking process, in which the cooking liquor is a mixture of sodium monosultite and bisulfte, and Whichalready contains a high ratio of sodium to sulfur, is treated With some alkaline soda compound and concentrated, and the resulting product is subjected to a reducing furnacing treatment under regulated conditions to produce-a furnace product containing a considerable proportion of the sodium as sodium sulfid, with the remainder of the sodium present mainly as sodiumcar-f bonate. Asolution of the sodium compounds of the furnace product is prepared which is utilized, either directly or after modification or further treatment, as a cooking' liquor in the sulid type of cooking process. Residual'liquor from the suld type ofcooking operation is concentrated, and the resultingeproduct is subjected to a suitable heating or furnacing operation to decompose organic compounds andto form a product containing the soda largelyas sodium carbonate;

anda `solution of .the resulting sodium com'- pounds is prepared and subjected to a regulated sulfiting treatment to regenerate asuitable cooking liquor containing sodium sulte and bisulite which is then utilized in the acid-suliite invention.

In thel treatment'of residual liquor lfrom such "acid-sulfite Cooking operation,`the alkaline compound or compounds added to react`with acid therein and to more firmlyix sulfur therein, may be sufficient only to neutralize the acid, but may-advantageously be type ofcooking operation of this somewhat in excess thereof.` Other and adl ditional suitable sodium compounds may be added, as desired, e. g. to increasel the ratio of sodium to sulfur compounds in the liquor. The alkaline compound added and utilized for combining With acid of the residual liquor may be contained in Aalkaline residual liquor from the suld type of cooking operaltion or present in one of the furnace prod ucts Which contains sodium carbonate or sodium carbonate and sodium suliid, as its main alkaline constituents. By utilizing residual liquor from the sulfid type of cooking process, or' a regenerated solution containing sodium sullid and sodium carbonate, the content of sulfur compounds will be increased as Well as the content of sodium.

The invention also includes improvement in the carrying. out of the furnacing operation of theregenerative treatment, so that the heat of the hot gases may be employed for generating steam for the cycle, and `so that some sulfur as Well as soda compounds may be advantageously recovered for reuse inthe cyclic and interrelated processes. p

The cooking liquor used in the -sullid type lof cooking process of the invention may vary made up mainly of sodium sulfid and sodium carbonate. With cooking liquors of this kind, i. e., containing little or no sodium hydroxide or sodium sulfite, it is desirable to have a considerableamount of sodium carbonate present, for example, an lamount such that the sodium present as sodium carbonate is approximately equal to that present as sodium sulid.- For example, for poplar w'ood'the cooking liquor may contain about 800 pounds of sodium sulfid and about 1087 pounds of sodiumcarbonate for 4000 pounds of Wood l(oven-dry basis) and for spruce Wood the cooking liquor may contain about 1000 pounds of sodium sulfid and about 1359 f pounds of sodium carbonate to 4000 pounds of Wood (oven-dry basis). In such cooking liquors the sodium or sodium oxide equivalent of the sodium sulfid and the sodium carbonate is approximately equal. WithV such cooking liquors the amount of'sodium sulfid charged into the digester, when chemical pulp is desired Without a further cooking or chemical or other treatment, should be at least about 18 per cent on the oven-dry weight of Wood'treated and preferably 20 per cent or more. In such a cooking liquor, the sodium carbonate appears to be activeto some extent and to assist in the cooking operation, but the sodium sulfid is mainly relied upon. .The

perccntagesabove referred to are for poplar Wood; for Wood such as spruce, a larger amount of active chemical is required, as illustrated in the above example.

Instead of using (for cooking liquor) a solution containing mainly sodium sulfld and sodium carbonate, such as is obtainable directly bydissolving the soda content of the product from the reducing furnace treatment of the neutralized liquor from the sullite type of cooking operation, the liquor may have some of its sodium carbonate converted into caustic soda, so that the cooking liquor will contain, for example, around ten parts of sodium sulid for every two to ten parts of -sodium/ hydroxide, and so that the total 'of sodium) suliid and sodium hydroxide will amount to at least around 16to 18'per cent on the weight of the Wood (oven-dry basis) 'when poplar Y. Wood is used, and larger amounts of Na2S and NaOI-I for other Woods, such as spruce. The presence of caustic soda enables the amount of sodium sulid to be educed. The caustic soda may be readi y formed from sodium carbonate by causticizing with lime, for example, by treating the solution of sodium carbonate and' sodium sullid With a .regulated amount of lime, as a part of the regenerative treatment.

A further improvement .in the sodium sulfid type of cooking liquor may be made by the formation therein or the addition thereto of sodium sulte, for example, from 5 to 15 parts of sodium sulfite top10 parts of sodium sulid. The sodium sullite appears to combine with some of the sulfur of the sodium sulid during the cooking operation. Cooking liquors containing Nah-SC3 alongwith NagS and NaOH produce pulp Which is more easily bleached to a good White than when sodium sulfid alone or sodium sulid and sodium carbonate are employed Without other calcium monosuliite, for example, during or.

as a part of the clarification. The reaction of such calcium monosulte with' some of the sodium carbonate produces sodium sullitein solution and a precipitate of calcium carbonate which aids -in the clarification of th liquor. 'l i By treating th solution containing sodium carbonate and sodium sulid with both lime and calcium sulte, in appropriate and regulated amounts, a cooking liquor can be produced which contains both caustic soda and sodium sull-ite in addition to sodium sullid; for example, with the sodium sul-iid present in preponderating amount that is to say, that more sodium is present as sodium'sulfid than as sodium hydroxide or as sodium sulte.

Where the sodium carbonate and sodium sulid liquorV contains considerably more sodium as sodium carbonate than asr sodium sulfid, the addition of suiiicient lime, or calciumsulfite, or both, permits ofthe ready reproduction of cooking liquors which contain a preponderatingamount of the sodium in the form of caustic soda, or 'in the form of sodium sulite, or of admixed caustic soda and sodium sulte, with a relatively smaller amount present as sodium sulfid.` Such cook- Ving liquors can be used in cooking processes in which a preponderance of sodiumsulite isdesired, or in which a preponderance of caustic soda is desired, or alpreponderance of caustic sodaV and` sodium sulfite over the sodium sulfd content.

In the liquors of the cooking operations of this invention, some other sodium compounds may be present, such as sodium sulfate, sodium thiosulfate, etc., but these are advantageously. kept lowin amount. They serve to combine some sulfur which is again available as sodium sullid aftera reducing furnace treatment.

. As examples of cooking liquors which coni basis).

For poplar wood the cooking liquor may `contain about 800 pounds of sodiuin'sullid,` about 1087 pounds of sodium carbonate, and about 322 pounds of sodium sulte '(NagSO). For spruce Wood the cooking liquor may contain aboutl 1000 pounds of sodium sulfid, about 1359 pounds of sodium` carbonate and aboutflOO pounds of sodium sulte.

. Where caustic soda is present in the cooking liquor, there may be present, for example, for poplar wood', about 600 pounds of sodium sulfid, about 815 pounds of sodium carbonate, and about 205 pounds of caustic soda. For spruce wood there may be present about l 5-0v pounds of sodium suld, about 1.020 pounds of sodium carbonate, and about 255 pounds of caustic soda.

The'following examples show the amountV in pounds of sodium sulfid` sodiumcarbonate, sodium suli'ite and caustic soda, where all these are present, either alone or with small amounts'of sodium sulfate,sodium thio-sulfata-etc., each example being for about 4000 poundsio'f wood, oven-dry basis.

. NazO as Sodium NazOas i Wood Sodium carbom Sodium Caustic sodium sodium suld sulte soda thio ate sulfate sulfate Poplar, Exhibit 1 600 300 322 205 80 Q 40 Spruce, Exhibit 2 750y 375 402 256 100 50 Poplar,Exhibit 3 640 544 258 164 127 64 Spruce,Exhibit 4 800 600 322 205 159 80 Pop1ar,Exhibit 5 v711 966 144. 92 71 71 rgpiaanxhibite 40o 20o 300 400 o0 50 Pine,Exhibit 7 615, k265 498 316 104 52 Pine,Exhibit 8 500 200 350 450 75 50 Where vthe regenerated solution, Icontaining mainly sodium sulfid and sodium carbonate, regenerated entirely or in part from Asodium carbonate into sodium sulfite and caustic soda and lwith formation of calcium carbonatel' Where, however, the ratio of sodium carbonate to'sodium sulfid is'such that the liquorI wouldlnot yield vcooking liquor of the desired composition, appropriate. additions may be made, 'o,r la part only of the regenerated (liquor utilized. with additions of.

l fresh material'.v Sodium sulfite, for example,

can beadded, -which may be made by subjecting toaisulting'ltreatment a solution of the sodium carbonate produced by the oxidizing furnace treatment hereinafter referred to, and this sodium sullite may be added and be present in the cooking liquor. In this way the desired ratio of sodium sulfite tosodium sulid can be obtained. An excess of sodium carbonate may or may not be present in such cooking liquor. A portion of the NagCOgNaigS liquor may be causticized to the required extent, another portion thereof maybe sulited and these two portions mixed after such treatments to form cooking liquor of the desired composition.

' In the cooking liquor of the acid sulfite type of cooking process of the lpresent invention, as pointed out above, an excess of free `sulfur dioxide beyond that corresponding to sodium bisulit-e is avoided and while an.

amount of SO2 corresponding to sodium bisulfite can be used, we consider it more advantageous in the cyclic and inter-related processes of the invention, to have a considerable amount of vsodium monosulte present in admixture with sodium bisulite. In regeiierating the acid sulte type of cooking liquors from the sulfid type of residual liquors, thc greater pa'rt of the sulfur content of the latter can be eliminated or oxidized during the oxidizing furnace treatment, but some sodium sulfid or thiosulfate may be present in the finished furnace product. Sodium thiosulfate may also be formed in the liquor when there is any sulfid present inthe liquor which is sulfited, particularly if the sulfiti'ng is done with ,sulfur dioxide. The

presence of sodiumthiosulfate is objectionable in a highly acid sulite of sodium cooking liquor, but by having a sufficient amount of sodium monosulite present in the cooking liquor in addition to the sodium bisulfite, a limited amount of sodium thiosulfate may be present therein" without su'ch objection, in f the way of sulfur separation, darkened stock, etc., as when it is present in a highly acid sulfite liquor having insufficient combined SO2. Accordingly, when sodium thiosulfate is present in a regenerated acid sulite type of cooking liquor, it is advantageous to regulate the 4composition of the cooking liquor so that it contains bot-h sodium monosulite and sodium bisulite, and so that a suiicient amount of sodium monosulte is present therein.

le give below a. series of examples showing the charges of sodium sulte'and of sodium bisulite in cooking liquors which 4may be used. In certain of these the cooking liquor is awsodium bisulite cooking liquor,

and in such case sodium thiosulfate preferably is absent. Such a liquor may be used,

lfor example, at the outset, or where, by

special treatment during regeneration, thiosulfate is absent. In the other cooking liquors of the examples it will be noted that sodium suliite is present in addition to sodium sodium sodium sodium lfosfgf Wood sulte bisulte sulfate ,ate

rlxagSOg) (NaHSOg) (l\a2SOI4) (Nazszoa) Poplar, Example 1 1, 200 495 Poplar, Example 2 1, 067 440 Spruce, Example 3 1, 333 550 Poplar, Example 4 .800 660 338 62 Spruce, Example 5 1, 000 825 422 67 Poplar, Example G v. 640 792 229 Spruce, Example 7.-.--- S00 990 286 Poplar, Example 8 1, 321 229 Spruce, Example 9 1, 651 286 Poplar, Example 10 1, 400 165 366 102 Spruce, Example 11-.-.- 1, 800 165 (157 127 Cooking liquors which contain a very high ratio of sodium to sulfite (high combined V SO2) release no considerable amount of sulfur' dioxide when the digester is relieved to promote liquor circulation during the cooking operation, and the residual liquors produced therefrom release little if any sulfurl dioxide when the digester contents are blown into a blowpit. Such liquors avoid such a liberation of sulfur dioxide as takes place when highly acid liquors are employed, i. e., containing a large excess of sulfur dioxide, and thus it is unnecessary to provide an elabcrate sulfur dioxide recovery system such as commonly used in the usual and common acid sulite cooking process using highly acid cooking liquor. Accordingly, a much higher proportion of the sulfur content of the cooking liquor is retained in the residual liquor 'and is thus available for the production of some sodium sultid during the subsequent treatment 'of constituents of this residual liquor.V

In order to make advantadeous use of its sulfur content during the siilbsequent treatment of the residual liquor, even though it be not strongly acid, suiicient alkaline residual liquor from the sodium sulfid type of cooking process or from another suitable alkaline cooking process, or 'suilicient other alkaline constituents, for example recovered soda compounds, are added to react With the acid and to fix or combine some of the sulfur as a sodium compound,.so that the treated residual liquor is rendered neutral or alkaline, i. e. to litmus. In case organic matter separates out when residual liquor isY thus y treated, this may be removed'in any suitable The liquor after neutralization or vbeing made alkaline is concentrated and the constituents therein are decomposed under suitable reducing conditions, so that arelatively large amount of the sulfur content of the residual liquor will be retained in the product as s0- dium sulfid. The remainder of the sodium compounds Will be mainly converted into sodium carbonate.

The reducing furnace operation, moreover, may be so carried out that the gases resulting therefrom are utilized. By regulating the reduc'ing conditions, the resulting gases contain carbon monoxide, and may contain a combustible sulfur compound or even elemental sulfur. Such compounds as COS, CS2 and ILS, and also elemental sulfur, yield sulfur dioxide or sulfur trioxide 0r a mixture of both when burned by the addition of further air. Inlorder to advantageously recover sulfur from'the furnacey gases, and also to utilize their heat value, these gases are employed as fuel, and then are subjected to treatmentr for the recovery of sulfur dioxide and of sulfur trioxide therefrom, which are thus made available for utilization in the process and correspondingly reducing the amount of fresh sulfur or sulfur compound otherwise supplied to make up for losses.

The sulfur lost may be replaced either by burning. sulfur, or in the form of sulfur doxide from some other source, or it can be supplied in part by adding sodiumsulfate before the reducing furnace treatment. Sul- The combustible matter in the residual liquor from the sodium sulfid type of' cooking operation is advantageously burned under high temperature and oxidizing conditions having a regulated excess of air. -The heat thus produced can be utilized ina boiler to generate steam for the cooking process. This oxidizing burning treatment serves. to separate from its combination with soda, a considerable part of which sulfur which is converted into sulfur dioxide or sulfur trioxide or a mixture of both, and such oxides can be recovered from the furnace gases. The oxidation treatment also converts a considerable part of the remaining sulfur Which is thus present in the furnace product in the form of sodium sulfate. Such furnace product will contain a high percentage of sodium carbonate, which lcan be dissolved and'readilysul-v l'ited to form the sullite of sodium type of cooking liquor. The sodium sulfate present therein will aid in supplying sodium suliid when the sulfitetypefof residual liquor is treated to regenerate the sodium sulfid type of cooking liquor.

The hot gases from the two types of furnaces, that is, the reducing tiype'of furnace and the oxidizing type .of furnace, are advantageously mixed, and a further amount of air, if required, supplied to burn combustible constituents which the mixed gases contain, and the resulting hot kgases can be passed through a steam boiler to utilize their heat..

Some solids collect in the various gas passages, e. g. of the boiler, which usually are high in sodium sulfate. A further amount of solids may be collected from the gases, and these solids also are usually high in sodium sulfate and can advantageously be added to the cycle before the reduction treatment which produces sodium sulfid. The furnace gases may also contain a considerable lamount of sulfur dioxide and of sulfur trioxide. Sulfur dioxide can be recovered by scrubbing the gases with a sodium carbonate solution. Sulfur trioxide when present will form sodiumsulfate, while sulfur dioxide will form sodium sulfite. These can be returned to the process, the sodium sulfite for use in the sulfite cooking. operation, and the sodium sulfate to produce additional sodium suld during the reducing furnace treatment. By employing two separate scrubbing treatments, a considerable separation of the S03 from the SO2 may be effected and advantage taken 4of such separation. i

`Where the sulfiting of the sodium carbonate of cooking liquor is carried' out in part by scrubbing the hot gases of the rnaces with v the liquor and in part by sulfur dioxide formed by the combustion of fresh sulfur, these operations can be so regulated that the amount of sodium suliite and of sodium bisulite in the resulting cooking liquor can be controlled. The sodium carbonate liquor can be used first for scrubbing the hot furnace gases (advantageously after removing a large art of the SO3 content thereof) and the sulntin'g can then be completed by passing the partially sulted liquor over an absorption tower into which a suitable mixture of sulfur dioxide and nitrogen, resulting from the combustion of sulfur in air, 1s introduced, the

temperature thereof being controlled so as to get good absorption without unduly cooling the liquor.

Instead of recovering sulfur dioxide or sulfur trioxide or both from the furnace gases by using a sodium carbonate solution, this recovery can be effected by using milk of lime,

`or an aqueous suspension of calcium carbonate (preferably recently precipitated),

and bringing'the gases into contact with the milk of lime or the aqueous suspension" so that sulfur dioxide and sulfur trioxide will be absorbed andforming calcium sulfit'e and calcium sulfate. If there isany acetic acid in the furnace gases it may form calcium ace'- tate, which may remain in solution, or may react with sodium compounds, such as sodium lsulfite or sodium sulfate when present to form calcium sulte or calcium sulfate, leaving sodium acetate in solution. The calcium sulfate and calcium sulte, where both are present, may be separated from thesolution and employed 'for treating some of the liquor containing sodium carbonate and sodium suliid to convert sodium carbonate into a corresponding amount of sodium sulfate or sodium sulite, or.b0th, and form calcium carbonate.

The admixed vcalcium sulfite .and calcium sulfate, where both are present, may be emp'loyed together for treating a sodium carbonate solution, or the calcium sulfate and calcium sulite may be separately utilized by treating the 'mixture with /only enough sodium carbonate Ato reactwith the calcium sulfate, leaving calcium sulfite behind with carbonate may be employed for sulfiting some I sodium carbonate, and the resulting sodiumA sulfte may be employedin a cooking liquor. By separating the sulfate and .the snulfite radicles in this way, thesulfate radicle is em-- ployedin that part of the'cycle whereit is best used, and the sulte radicle is transferred to that part of the process where it is best used. The calcium suliteL may, however, be

used for sulfiting" some sodiumcarbonate of Y the ,liquor which is to be used in the sulfid type of cooking process, where this cooking liquor is to contain sodium sul te, aswell as sodium sulfid. The sulfate radicle which is A returned to the process may be in part recovered as sodium sulid for the sulfld type of cooking process, of the sulfate radicle may be transferred, sep- While part of the sulfur arated and recovered as the sulite .radiclel from the furnace, gases sonthat it may be .utilized in producing sodium sulfite. v y

VThe inter-related processes of the invention and the novel steps and features of the regenerative and interrelated processes will be further described and illustrated in connection with the 'accompanying drawing, which is 'a low-sheet in amore or less conventional and diagrammatic manner and with certain of the operations indicated thereon. It will be understood that the invention is illustrated by but is not limited to the particular operations and sequence of operations illustratedin the flow-sheet. Moreover, certainl of the features of the invention are4 not limited to use in the particular 'cycle and sequence of steps of the `are indicated as entering at 18, and the cooking liquor through 20, this cooking liquor being that regenerated from the sulfid type of processas herein described. The relief line indicated at 19rmay'be employed to promote circulation of the cooking liquor by the steam which enterslthrough 21. The steam sodium compound.

may come from the waste-heat boiler through the line 23, or other steam may be supplied through the line 22. Vhen the cooking operation has been completed, the contents of the digester are blown through the line 24 into the blow-pit 2, provided with relief 25. Wash water, which may be the condensate from the evaporator 4, enters at-26, or other water,l may be employed. The washed pulp is separated at 28 and the mixture of residual liquor and wash water passes through the line 29 into the mixer 3. Sodium compounds to make up for losses may be added at 30, for example, sodium sulfate or other suitable A n alkaline liquor is added at 31 to neutralize uncombined sulphur-containing acids in the residual liquor. This alkaline liquor may be a portion of the residual liquor from the suld type of digestion process, as indicated by the line 31, or some of the liquor from the dissolver 6 or from the clarifier 7, may be employed, as indicated by the line and 51. Part of the alkaline material for neutralizing the acidity may come in part from each of these sources, thus .providing flexibility and control.

The'ad-mixture of acid residual liquor and .alkaline liquor is agitated and thoroughly mixed in the tank or mixer 3. Any libeiated gas, such as carbon dioxide, may escape as indicated at 32. Lines 84,85 and 86 show the return of solids collected from the gas passages ofthe boiler 14 and dust collector 15.

The solids thus returned are generally high in sodium sulfate content-and are thus incorporated and admixed with the liquors for treatment in the subsequent reduction kstep to form sodium sullid..y

, In case the admixed liquors contain an objectionable amount of suspended solids, the

liquor may be clarified before passing it from the mixer 3 to the evaporator4. v

The evaporator4 may be any suitable type of multiple e'ect evaporator and is advantageously equipped with means for forcing a rapid circulation of liquor through the heating portion of the mostA highly concentrated eect. A regulated amount of caustic soda may be added to the mixed liquors to redissolve precipitated organic compounds,

Vand this when so employed is preferably added after carbon dioxide has been permittedy to escape, which carbon dioxide may be produced by interaction between the acids of the residual liquor and the sodium carbonate of the alkaline liquor added, and preferably after removal of most of the suspended organic matter.

, Cooling water is shown entering the evaporator through 34, and steam enters through 35. Condensates leave through 36, that which is not reused being rejected through 36. The steam is shown as entering through 23 and 35 and being obtained from the boiler 14. Any other suitable source of steam may be employed in whole or as a part thereof in case it should be needed.

The hot and highly concentrated liquor passes through 37 into the reduction furnace 5, in which the organic matter'is consumed and a furnace product containing mainly sodium carbonate and sodium sulid is produced. Any suitable type of furnace may be employed for this step, and it is an advantage to so conduct the operations in the furnace 5that a high percentage of the soda in the furnace product is present as sodium sulfid, and that the amount of lsodium sulfate is small. A product which carries about 40% to 50% of its sodium in the form of sodium sulfid and about an equal amount in the form of sodium carbonate is quite suitable.

-The ratio of suld to carbonate will vary .somewhat due to operating conditions. Poly- -sulfides are advantageously absent in the fur- .desirable for retention-'of sulfur and theformation of sodium suliid", and the CO can be burned to CO2 for heat utilization in boiler 14. The returned gases aid in restraining the temperature in 5 and are thus of additional advantage. The gases from 5, which are generally and advantageously combustible, e. g. containing considerable CO, are shown passing through 38 and thence through 81 into boiler 14. Oxygen for the combustion of CO, and of sulfur or unoxidized sulfur compounds, e. g. CS2, COS, HQS, may enter through line 80 as air, in case more oxygen is required than enters with the gases coming from furnace 12 through line 67. The amount of air thus added can be controlled so'as to convert C0 to-COZ, oxidize sulfur compounds to SO2 or S03, and the heat thus generated can be utilized ingenerating steam in boiler 14.

Furnaces and'12 may be so arranged as to receive their respective charges of' re sidual liquor in the form of atomized liquor,

one operating with an .insuicient supply of air and the other With an excess supply of air, the furnace being operated so as to conserve sulfur therein and yield a furnace product high in sodium sulfid, While the furnace 12 is operated so as to drive oif a considerableamount of sulfur and yield a furnace product high inA sodium carbonate and low in sodium-sulfur compounds, and With such sulfur compounds as present being largely in theform of lsodium suliite orsodium sulfate. The returned gases referred to may, at least in part, being introduced adjacent the highly heated Walls, and roof, so as to maintain, as well as feasible,l these portions of the furnace at safe Working temperatures.

The furnace product from 5 is shown passing through 42 into dissolver 6, and Water or condensate from 4 enters through 43. Line' 44 shows how some caustic soda or sodium sulfid, for examples, may be added yto the liquor in the dissolver, forinstance when these are available for replacing lost soda in Wholeor in part. Also lime, calcium sul ite, etc., may be there introduced. Whenl the liquor in thel dissolver is of appropriate strength, it passes through 45 into clarifier 7, of any suitable kind. I

Some lime, suiiicient to convert the required amount of sodium carbonate into caustic soda,`

or/and` CaSO3 sufficient in amount to convert the required amount of sodium carbo-nate intotsodium sultite may be added through 46, -and thoroughly admixed with the liquor. Prior to adding such ycalcium compounds, a regulated portion of the liquor from 6 may be diverted through 45. The liquor is clarified in 7, separated from the solids, and the solids Washed by introducing wat-er through 47. The Washed solids leave through 49 and the clarified liquor and Washings leave through 50. The Washings may, if desired, be kept separate and returned to the dissolver 6. Some of the clarifiedl liquor may be diverted tliroughv- 51 as stated.

The clarified liquor from 7, consisting mainlyof sodium sulfid as active cooking reagent (with which maybe present a moderate amount of either or both sodium sulfite or caustic soda) and which may contain considerable sodium carbonate (but preferably free from sodium polysulfid and free from or l, low in sodium thiosulyfate) lis shown passing through 50 into digester 8 Where it is employed as a cooking liquor, the predominating amount of digesting being due to the sodium suld. Wood chips enter the digester 8 through 52. 53 is .a relief line which may -be employed toassist in circulating the cooking liquor. Steam enters at 54, and may come through 55, from any suitable source, or through B88 and 87 from the boiler 14. Surplus or unused steam from'the boiler14 is shown passing vbeyond through 56 to any other suitable point or usage.

When the sodium sulfid digestion step has been completed, the contents are discharged through 57 int-o blo-Wpit 9, provided with relief 58. The stock is lthen delivered through 59, advantageously after thinning with some 'residualliquor While in'the blow-pit or being removed therefrom, into the Washing device, of any suitable kind but preferably one that Will Wash-the stock and remove the liquor in an economical manner and produce a Weak black liquor containing all or nearly all of the soda Without an. excessive dilution.

`VVater for Washing the stock enters through 60, Which may be fresh Water?l supplied through 60', or condensate from the evaporator 11 through lines 65 and 60. The

Washed pulp passes out through 61A, and the;

through 65.

The highly concentrated liquor leaves the evaporator through 66 and is charged into the oxidizing or burning furnace 12. This furnace may be of, any suitable type. It may operate by atomizing or spraying the strong and het black liquor into it, the Water being evaporated and the organic matter decomposed and carbon burned to CO, and preferably to CO2 to a large extent at least. An excess of air over that theoretically required for complete combustion may be introduced, e. g., through 69 and 69. Some of the products of combustion may be returned to the furnace, e. g. through 70 and 70', coming from the scrubber '16 through 91, 93 and 70. Some of these returned gases may be admixed With air by passing through line 71, thus giving a modified air which may serve to suppress the ame temperature in the furnace so as to'aid in maintaining the furnace at a safe Working temperature. Another portion of such returned gases may be-introducedinto the furnace adjacent the hot Walls, roof, etc., as a further means of maintaining safe Working temperatures, these hot gases absorbing heat as their temperatures are raised. The mixture of hot gases from this for use in the cycle of operations.

The soda product of the furnace, mainly sodium carbonate (with some sodium sulfate and little if any NagS) passes through 68 into dissolver 13. Water is shown entering through 72, which may be fresh water through 75 or condensate through 74 and 65.

73 shows how sodium carbonate,sodium sul- 1 liquor containing` the required amount of combined and uncombined sulfur dioxid, e. g., a solution which contains both sodium monosultte and bisultite. lSulfur for supplying the sulfur dioxide required, in additionto that already in the gases coming from the dust collector l15, is shown as SO2 entering at 90. This may be obtained by burning sulfur in air to form a mixture of SO2 and nitrogen, these gases passing through or iron sultides or other suitable sulfides may be roasted to form SO2 and this SO2 be passed through 90. The scrubbed gases leave the scrubber through 91, and the unreturned gases pass out through 92,'e. g. to a suitable stack.

The sulfited liquor containing the desired amount of combined and uncombined sulfur dioxide, and which may also contain some acetate or other soluble organic acid radicles removed from the gases by the `scrubbing operation, passes through 77 into the clarifier 17 and the clarified liquor passes through line 2O to the digester 1. Water is shown entering at 7 8 to wash the sediment removed from l the liquor in 17, and the washed sediment leaves through 79, the washingsibeing added to the liquor. l

The hot gases entering the boiler carry some soda and also some sulfur oxides, a part of which comes from the furnace 5 and a part from the furnace 12. Some sodium sulfate is caught in the boiler flues, etc. This is removed through 84, as stated above.

. as stated.

This dust collectormay be of any suitable type, but it is advantageously so operated as to recover substantially all of the soda, which 05 is primarily present as sodium sulfate in many cases, and permit the sulfur dioxide to pass on to the scrubber 16 along with the gases which pass from 15 through 89 into 16. An electrical precipitation apparatus may serve as the dust collector7 and it may with advantage be operated at a' temperature conysiderably above the dewpoint of the gases,

and thus recover nearlyall of the soda as a dry product, which, as stated, contains considerable percentages of-sodium sulfate.

Thus a considerable amount of the sulfur which is eliminated fromsoda, e. yg. by the oxidizing combustiondtreatment in furnace 12, is collected. as sodium sulfate and is returned to themilxer' to be employed for the production of sodium sulfid. And a further amount of sulfur as sulfur dioxide, which may come in part from the reducing furnace 5 and in part from the furnace 12, is collected in the scrubber .and thus Vserves to make cooking liquor containing sulites. In\one type of cooking liquor the sulfur is active as sodium sulfid, while in the other it is active as an Oxy-sulfur compound, i. e. a suliite. And. the cycle of operations is so carried out that the sulfur is in one' instance employed as a sullite while in another instance it is employed as a suliid, and the two types of cooking operation and their residual liquor treatment cooperate in an advantageousmanner. The inter-relatedprocesses of the present invention are noty limited to processes in which the cooking opera-tions are carried so far that chemical pulpl is produced. The cooking operations may be of relatively short dura-tion, and with lessy chemicals than will completely pulp the wood and produce chemical pulp, and the cooking operation may be stopped when the wood has been sufficiently softened to lend itself to a mechanical treatment, whereby a strong pulpy mass is produc-d with high yield of product. f The digestion steps of the inter-related processes may thus be partial digestion steps in which the wood is softened and only partially cooked, and in which they subsequent treatment of the partially cooked or underdone pulp is a mechanical treatment,or a treatment by some other pulping process, which may be a chemical pulp-making step.v 4 The product thus made by the sulfid typel of cooking operation, when the process 1s carried out at a temperature around o to 150 C., and with only sufficient chemicals to'partially cook the wood may be employed for board manufacture. During such preliminary or partial cooking operations, the sodi-- um sulfid appears to act upon certain more readily reactable constituents ofthe wood, .d -and is itself converted to a considerable extent into sulfur-containingY organic compounds of such a character that sulfur can be readily driven olf when combustible constituents of the concentrated liquor are subjected v to a suitable burning nder oxidizing conditions. The residual liquor from such a sodium sulfid type of cooking operation appears to behavedifferently from other alkaline resij dual liquor from pulp-making operations.

In particular, it appears to intumesce to a less extent when the residual liquor is dried and the organic compounds are decolnposed. This appears to'explain why the soda is so easily' recovered therefrom. `V'Vith residual liquors produced by partial cooking operations of the kind above mentioned, additional fuel may be employed in the burning operation, if necessary or desirable, especially when the amount of organic matter in the residual liquoris not sufiicient to generate the desired amount of heat.

When the sodium sulid type of cooking operation is carried to completion, that is, so far as to produce chemical pulp, the pulps produced are sometimes dark, particularly Where the cooking liquor contains sodium sulfid and sodium carbonate, Without, or with only small amounts of, caustic soda or sodium sulfite. Such pulps may be given an auxiliary treatment to improve their color, or to improve their bleachability. For example, such pulp, after separation from the residual hquor and Washing, may be Washed with a Weak acid liquor, and for this purpose, residual liquor from an acid sulfite cooking operation may be employed, particularly a liquor which still has a distinct acid reaction. Or the pulps may be treated with hot liquor which contains a small amount of caustic soda, or a hot solution containing sodium sulfite may be employed. Some of the dark colored compounds are. thus removed from the pulp or are changed into other forms or compounds with resulting improvement in appearance and in some cases in quality of the pulps produced. The pulps produced when the sodium sulfid is accompanied by a considerable amount of sodium sulfite are of better color and quality, particularly where a rather large charge of sodium sulfite is also present.

Some of the pulpsobtained bythe sodium sultid type of cooking operation do not bleach readily to a high White by a single stage bleaching treatment, using chloride of lime bleaching liquor. Such pulps may be more readily bleached by first treating them with about ten to fifteen per cent of bleach (35% available chlorine), then Washing the resulting pulp products and adding a sufiicient further amount of bleach thereto and finishing the bleaching operation in the second stage with final Washing of the bleached product.

Pulps may be obtained from raw cellulosic materials other than Wood, in accordance with the cycle of the present invention. Thisapplication is in part a continuation of our applications Serial Nos. 686,137, led

A January 14, 1924; 704.176, filed April 4, 1,924,

and 456,187, filed Mar'ch 28, 1921.

Te claim: 1. The process of producing pulp from wood which comprises digesting Wood in aA cooking liquor containing most of its soda in the form of a sulfite of sodium, subjecting resulting residual liquor to a treatmentl including a reducing furnacing operation adapted to yield a product cont-aining sodium carbonate and a relatively large amount of sodium sulfide. utilizing sodium sulfide of the furnace product in an alkaline cooking liquor to cook an additional amount of Wood, subjecting residual liquor from the second cooking operation to a treatment including a furnacing operation adapted lto yield a product containing sodium carbonate and a lesser proportion of sodium sulfide than Was present in the alkaline cooking liquor, subjecting the furnace productito a treatment including a sulliting operation adapted to produce a cooking liquor containing an amount of sodium mono-sulfite at least equivalent to any sodium thio-sulfate which may be present; A

amount of sodium sulfide, subjecting the furnace product to a treatment including causticizing of sodium vcarbonate therein to produce an alkaline cooking liquor containing sodium hydroxi de and sodium sulfide, digesting Wood with the liquor so formed, subjecting residual liquor from this second cooking operation to a treatment including a furnacing operation adapted to drive off sulfur and produce a furnace product having sodium carbonate and substantially less sodium sulfide than was present in the alkaline cooking liquor,

subjecting the furnace product to a treatment including a sulfiting operation to produce a cooking liquor containing an amount 'of sodium mono-sulfite at least equivalent to any sodium thiosulfate which may be present; and repeating the cycle, utilizing the cooking liquor so formed.

3. The .process of producing pulp from Wood which comprises digesting Wood in a cooking liquor containing an acid sulfite of sodium and free from excess sulfur dioxide, separating the residual liquor from the pulp, neutralizing the liquor by the addition of an alkaline sodium compound, concentrating and treating the residual liquor to decompose v organic compounds under reducing conditions to obtain a soda produc-t containing mainly sodium carbonate and a relatively high content of sodium suld, forming therefrom a cooking liquor relatively high in sodium sulfid and cooking Wood therewith, separating the pulp fro/m the'residual liquor thus produced, concentrating and subjecting the residual liquor to treatment under oxidizing conditions to decompose organic compounds and obtain a recovered` soda product `containing mainly sodium carbonate, and

comprises cooking Wood with a cooking liquor containing sodium suliid as' its primary cooking chemical, cooking Wood With an acid sulfite cooking liquor containing a sulite of sodium, and treating residual liquor from one of saidrprocesses to produce cooking liqv uor for the other process and vice versa.

5. The---metliod of producing pulp which comprises cooking Wood With a cooking liquor containing sodium suliid, cooking Wood i With a'cooking liquor containing sodium bisulfite and sodium monosuliite, and treating residual liquor from each of said processes to regenerate cooking liquor for the other pocess.

6L The method of producing pulp which comprises digesting Wood `with a cooking -,liquor containing sodium bisuliite `as the principal cooking reagent and a lesser amount.

of sodium mono-sulfite, digesting Wood with an alkaline cooking liquor containing alkaline sodium compounds and treating residual liquors from each of said processes to regenerate cooking liquor for the other process. v

7 The method of producing pulpwhich comprises digesting- Wood with an acid cookingliquor containing sodium bisuliite as theprincipal cooking reagent, treating residual liquor therefrom to form a non-acid-liquor containing a sodium-sulfur compound, digesting Wood with the non-acid cooking liquor so formed, treating residual liquor from this second cooking operation to form a product coiitainin alkaline sodium compounds, subjecting this roduct to a treatment .including sul'fiting to` orm a cooking liquor for use in `the rst named'digesting operation containing sodium bisulite and more sodium monosulte than sodium thiosulfate; and repeating the cycle using the cooking liquor so formed.

8. The process of treating residual liquor.

resulting from cooking wood with a cooking liquorwhich contains sodium sulfite and sodium bisulite, which comprises addin there- Y to a non-sulfur-containing compoun ,60.

of sodium which is capable of reacting Withanv acid constituent therein, and subjecting the treated 4liquor to concentration and solid constituents thereof to a reducing furnace" treatment whereby a. product is formed which contains sodium carbonate and sodium sulfd.

9. In claim 8, the im roved step Which includes employing an al aline residual liquor for treating the residual liquor from the acid sullite type of cooking operation..

10. VIn claim 8, the improved step which is characterized by' regulating the addition of alkaline sodium compound to the acid sulfite type of residual liquor, whereby the treated liquor is rendered non-acid in character.

l1. The method of producing pulp which comprises cooking Wood with a cooking liquor containing sodium sulid, subjecting residual liquor from sucli process to treatment including concentration and .furnacing to form a product containing relatively less sodium sulderived and containing the sodium thereof mainly as sodium carbonate',.sulting a-solution of the resulting sodium compound so as to produce acooking liquor containing most of its soda in the form of a sulte of sodium, and cooking Wood therewith.

12. A cyclic process .for producing pulp from Wood, which comprises cooking a portion of the Wood in a liquor comprising a' sulfite of sodium, separating the residual" liquor from the resulting pulp and subjecting it to a treatment vvhich includes a furnacing of the solid constituents thereounder reducs ing conditions, cooking a second portion of the Wood in a liquor comprising sodium hydroXide and a sodium-sulfur compound derived at least infpart fromthe said solid constituents, separating a residual liquor from the resulting pulp, subjecting the residual liquor to a treatment which includes furnacing the solid constituents thereof under con- 13. In claim12, the-further improvement whereby the dust` recover treatment -is conducted at a temperature a ve the dew-point of the gases.

14. In .claim 12 af further improvement whereby sodium carbonate recovered from the f second urnacing treatment i`s utilized for scrubbing the gases and the sodium sulfte formed thereby is utilized in producing a cooking liquor suitable :forI use vin the first cooking treatment, andsubsequently divestf ing a portion ofwood by means of coo 'ng j liquor thereby produced.' 15. The improvement in the production pf cooking liquors from. furnace products containing soda mainly as sodium carbonate and with a small amount of sodium sulid, whichn comprises sulting-a solutionof such coinpoundsA under conditions to form a liquor isc . which comprises containing sodium bisulfite and sodium monosulite, with the amount of sodium monosultite in excess of the amount of any sodium thiosulfate which may be present.

16. The improvement in the treatment of residual liquors from pulp-making processes in which a sodium sulfid-containing cooking liquor` is employed, which comprises `subjecting the residual liquor to concentration and to furnacing under conditions to drive off sulfur and to form a product containing the sodium compounds mainly as sodium carbonate, and recovering sulfur dioxide from the furnace gases by absorbing it in a solution containing the sodium carbonate so produced, thereby producing a sullite of sodium, and digesting Wood with liquor containing the sulfite thus recovered.

17. The method of producing pulp which comprisescooking wood with a cooking liq- -uor containing sodium sulfid, subjecting resulting resldual l1quor to concentratlon and constitue-nts thereof to a furnacing treatment under conditions to drive ollik most o-f the sulfur therefrom, recovering a sodium sulfate from furnace gases so formed, adding it to residual liquor from a sulite cooking process, and subjecting such sullite residual liquor to a furnacing treatment under reducing conditions to form a product containing sodium sulfid and regenerating cooking liquor for the first mentioned cooking'operation from soda contained in such product.

18. The improvement in the treatment of residual liquors from a pulp making process in which a sodium sulfur compound is employed, which comprises subjecting constituents obtained from the residual liquors of lsuch a process to a furnace treatment to rcmixture with air to pass t-hrough said furnace during the treatment, whereby the treatment can be regulated. a

19. The improvement in the treatment of residual liquors from a pulp making process, subjecting constituents thereof including sodium and Oxy-sulfur compound to a reducing furnace treatment under conditions to produce a product containing a large amount of sodium sullid, and returning furnace gases to such reduction :furnace for admixture with the air to aid in regulating the treatment.

20. The improvement in the treatment of residual liquors, which comprises subjecting solids of a residual liquor including a sodium-sulfur compound produced by a cooking process in the manufacture of pulp to an oxidizing furnace treatment, subjecting constituents of residual liquor from a sulfited sodium cooking process to a reducing furnace treatment, admixing resulting gases from said furnacing operations and burning combustible material therein, collecting non-gascous material from the gaseous products of combustion and returning the same for treatment in the reduction step of the process.

21. In a process for producing chemical pulp from Wood,the steps which include cmploying sodium as a sullite in an acid sulfite type of cooking liquor which contains sodium bisuliite but is free from excess sullfurous acid beyond the bisulfite combination, and subsequently employing some of the same soda as an alkaline sodium-sulfur compound in an alkaline cooking liquor.

22. In a process for producing chemical pulp from Wood, the steps which include employing sulfur as a sulfite of sodium in an acid sulfite type of cooking liquor which contains sodium bisulte but is free from excess sulfurous acid beyond the bisulfite combination, and subsequently employing some of the same sulfur as an alkaline sodium-sulfur compound in an alkaline cooking opera.- tion.

28. Ina cyclic process for produc-ing chemical pulp, the steps which include cooking Wood and a cooking liquor `Which contains sodium bisulfite but is free from sulfurous acid beyond the bisulite state, and cooking Wood With an alkaline cooking liquor which contains an alkaline sodium-sulfur cornpound, some of each type of the cooking liquors being regenerated from soda contained in residual liquor from the cooking operation With the other type of cooking liquor.

24. In claim 23, the further steps characterized by mixing some residual liquor from one type of cooking operation With some residual liquor from the other type of cooking operation, subjecting constituents of the mixed liquors to a furnacing treatment whereby alkaline sodiun compounds are obtained, preparing a solution which contains these sodium compounds, and employing some of the solution in the preparation of cooking liquor for one of the cooking operations.

In testimony whereof We aflix our signalov 

